Imaging findings of immune checkpoint inhibitor associated pancreatitis

To describe contrast-enhanced computed tomography (CECT), 18-Fluorine (¹⁸F)-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT and magnetic resonance imaging (MRI) findings of immune checkpoint inhibitor (ICI) associated pancreatitis in patients undergoing immunotherapy for solid malignant tumours.

In this retrospective study, 25 patients with clinical and/or biochemical evidence of pancreatitis who underwent CECT, MRI and ¹⁸F-FDG-PET/CT while being treated with ICIs were included. Imaging features of acute pancreatitis included: pancreatic enlargement, heterogeneous enhancement, peripancreatic stranding, fluid collection, pseudocyst, necrosis, atrophy and calcification. ¹⁸F-FDG PET/CT imaging was reviewed for pattern of abnormally increased pancreatic FDG uptake. ICI-associated pancreatitis diagnosis was based on clinical, imaging and biochemical findings.

Imaging findings of ICI-associated pancreatitis included diffuse (n = 14) or focal (n = 11) pancreatic enlargement; heterogenous enhancement (n = 21); focal (n = 9) or diffuse (n = 15) peripancreatic infiltration on CECT and MRI. A pattern consistent with acute interstitial pancreatitis was present in 20/25 (80 %) patients, and a pattern consistent with autoimmune pancreatitis in 4/25 (16 %). A mixed pattern was present in one patient (4%). No patient developed necrotizing pancreatitis or a pseudocyst. The CT severity index was < 3 in all patients, consistent with mild pancreatitis. Focal pancreatic FDG uptake was noted in 2/3 (66 %) of patients. Acute imaging findings resolved with treatment in all 25 patients. Pancreatic atrophy developed in 11/25 (44 %).

ICI-associated pancreatitis typically presents as either focal or diffuse acute interstitial pancreatitis. Post-pancreatitis atrophy is common. The ICI-associated pancreatitis cases in our study were mild, managed conservatively and did not result in local acute complications.